Downhole tool

ABSTRACT

A downhole tool comprises a body having a slot therein, a cutting blade mounted within the body and extendible and retractable through the slot such that the outer diameter of the tool can be selectively increased, an actuation member for driving the cutting blade between the retracted and extended positions and a mounting means connecting the blade to the actuation member, said body having a tapered surface along which the blade travels such that as the blade travels along the tapered surface the blade moves radially outwardly with respect to both the body and the mounting means whilst remaining in contact with the tapered surface.

This invention relates to a downhole tool and more particularly to a tool for expanding the inner diameter of a bore, most particularly a well bore, and more specifically to an underreamer and more particularly to an underreamer for use in enlarging the diameter of a bore-hole, more particularly of a bore-hole for use in the extraction of hydrocarbons from a sub sea or subterranean well or other fluids and gasses.

When drilling wells, such as for example oil and gas wells, typically concentric casing strings are installed and cemented in the borehole as drilling progresses to increasing depths. Successive lengths of casing string are supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas is reduced.

Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it is often desirable to enlarge the borehole below the terminal end of the previously cased borehole. By enlarging the borehole, a larger annular area is provided for subsequently installing and cementing a larger casing string than would have been possible otherwise. Accordingly, by enlarging the borehole below the previously cased borehole, the bottom of the formation can be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.

Underreamers are used in the oil and gas industry to enlarge the diameter of a borehole such as a well bore, particularly below a restriction in the bore. A typical underreamer has a tubular body with a plurality of arms, which can be selectively retracted into or extended from the body of the tool. This allows the underreamer to adopt either a retracted outer diameter where it can be passed through casing strings such as described above or an expanded outer diameter where the outer diameter can be greater than that of the casing string through which the underreamer has been passed in the retracted condition.

Each of the arms is provided with a series of cutting elements such that extension of the arms from the body of the underreamer brings the cutting elements into contact with the inner surface of the well bore. Rotation of the underreamer with the arms in the extended position removes material from the wall of the well bore and results in enlargement of the inner diameter of the bore.

Hydraulic underreamers are known in which a hydraulic fluid is pumped into or out of a reservoir in the body to push the arms of the underreamer into the expanded position. Such tools are prone to problems in which the hydraulic lines become blocked or the hydraulic actuators such as rams can become jammed with entrained material which can cause the arms to become jammed in the extended position, or alternatively, prevent the arms from moving into the extended position for operation.

Furthermore, typical underreamers have the cutting arms pivotally mounted on the body. A pivot pin is passed through a bore in one end of each cutting arm and then secured in a fixing in the body of the underreamer.

Each cutting arm is housed in a recess in the body of the underreamer which matches the shape of the arm. Upon actuation, the cutting arms are pivoted from the stored position within the recesses about the pivot pins, and extend outwardly from the recesses in the body thereby increasing the effective outer diameter of the tool.

As the underreamer is rotated in the expanded condition, the cutting arms remove material from the inner wall of the well bore to increase the inner diameter of the well bore. The material which is removed from the wall of the bore must be removed from the bore and can, in some cases, become entrapped between the body of the underreamer and the extended arms which can prevent the arms from pivoting back into the recesses in the body and thus prevent the underreamer from returning to the stored condition.

It is a further problem that the pivot pins of such pivoting arm underreamers can be subject to high stresses and any jarring of the expanded arms of the underreamer is transferred through the pivot pins to the body. Therefore the pivot pins must be capable of withstanding such conditions otherwise they represent a weak point in the tool.

In such cases where the underreamer fails, it is necessary to recover the tool from the well bore which typically involves a fishing operation which is both costly and time consuming, especially where such an operation generally involves the recovery of the tool from hundreds or thousands of meters below the surface.

A further known underreamer comprises a mandrel incorporating an angled ramp on the outer surface. The mandrel moves longitudinally relative to the arms which causes a mounting block upon which the arms are supported to move along the ramp thereby lifting the arms out of the body of the tool at an angle of 90°. To retract the arms, a spring is provided below the mounting block and mandrel. In operation this spring has to overcome the weight of the mounting blocks and mandrel and also the seal friction and other losses which has not proven effective.

A further known underreamer proposes a plurality of cooperating angled groves and ribs formed in the sides of the cutting arms and the body of the underreamer. The arms are biased into the lower (closed) position by a spring provided above the arms. As the arms move along the body into the extended position, they lift out of channels in the body and the spring is compressed. When the cutting operation is completed, the slide back into the retracted position. In practice however, mud and debris can become entrained in the groves and can prevent the arms from successfully retracting.

It is an object of the present invention to provide an underreamer which has a simple design with few moving parts and which addresses the problems of material removed from the wall of the well bore becoming entrapped between the cutting arms of the underreamer and the body of the tool.

According to one aspect of the present invention there is provided a downhole tool comprising a body having a slot therein, a cutting blade mounted within the body and extendible and retractable through the slot such that the outer diameter of the tool can be selectively increased, an actuation member for driving the cutting blade between the retracted and extended positions and a mounting means connecting the blade to the actuation member, said body having a tapered surface along which the blade travels such that as the blade travels along the tapered surface the blade moves radially outwardly with respect to both the body and the mounting means whilst remaining in contact with the tapered surface.

Advantageously the tool comprises a plurality of slots and a plurality of cutting blades, each blade being extendible and retractable through a respective slot in the body.

Preferably the or each slot in the body extends longitudinally along the length of the body.

Conveniently in the case where a plurality of slots are provided in the body, these slots are equispaced around the outer surface of the body.

Preferably the mounting means comprises a generally rectangular block, which is formed with a T-slotted head at one end.

Preferably the cutting blade comprises a recess at one end which receives the T-slotted head of the block.

Advantageously the depth of the or each cutting blade is greater than the depth of the block.

Preferably the cutting blade(s) and body are slidably connected together.

Preferably the or each blade is fixed along one longitudinal edge to the body.

Conveniently a channel is formed in one of the underside of the cutting blade and the tapered surface of the body and a cooperating leg is formed on the other, the leg being slidably constrained within the channel to prevent the blade being lifted out of engagement with the body as the blade slides longitudinally along the tapered surface.

Conveniently, the mounting block further comprises a jetting nozzle. This allows fluid to be selectively jetted through the tool during operation.

Advantageously, the mounting block is fixed to the actuation member.

Most preferably the block is bolted to the actuation member.

Preferably the actuation member is a sleeve. Most preferably the sleeve is slidably mounted within the body of the tool and is selectively operable between a retracted and an extended position within the body.

In one embodiment the sleeve is operated by a drop ball mechanism.

Advantageously the tapered surface forms a ramp and most preferably the ramp is a linear ramp.

According to a further aspect of the present invention there is provided a method of moving the cutting blade of a downhole tool between a retracted position in which the blade is stored within the body of the tool and an operative position in which the blade extends from the outer surface of the tool comprising the steps of moving the blade longitudinally along a tapered surface within the tool such that the blade extends through a slot in the surface of the tool.

One aspect of the present invention will now be described with reference to and as shown in the accompany drawings:

FIG. 1 is a schematic perspective view of a downhole tool according to one aspect of the present invention in a retracted condition;

FIG. 2 is a further schematic perspective view of the tool of FIG. 1 in an extended condition;

FIG. 3 is a schematic view of an inner mandrel of the tool of FIG. 1;

FIG. 4 is a perspective view from one end of a cutting blade of the tool of FIG. 1;

FIG. 5 is a perspective view from the one end of the cutting blade of FIG. 4, and

FIG. 6 is an enlarged view of the cutting blade shown in the operative condition of FIG. 2.

Turning now to the drawings, FIG. 1 shows an underreamer 1 according to one aspect of the present invention. In this figure the underreamer is shown in the closed position. The underreamer comprises a substantially tubular hollow housing 2. The housing has one or more longitudinal slots 3 through which a cutting blade 4 can extend. In the embodiment shown the housing has three longitudinal slots which may be equispaced around the body and thus would allow three cutting blades to be selectively extended from or retracted into the body as will be described further below.

The longitudinal slots 3 have a depth which is sufficient to extend above the cutting blade when the blade is shown in the retracted position of FIG. 1 such that the blade does not break the surface of the slot in this condition.

A substantially tubular mandrel 5 is mounted within the body of the underreamer. The mandrel comprises a shaft 6 at one end as best shown in FIG. 3 and has an annular collar 7 formed around the outer surface part way along the shaft.

The annular collar has a greater outer diameter than the shaft and an annular rim 8 is formed between the outer surface of the shaft and the outer surface of the collar. The annular rim 8 of the collar provides an abutment surface for a spring as will be further described below.

One end of the shaft terminates in a substantially solid body 9 which has a generally tubular form with a larger outer diameter than the shaft. The junction between the shaft and the solid body provides a shoulder 10 as will be further described below.

One or more tapered regions 11 are formed in the body and extend from the junction of the end of the body adjacent the end of the shaft along the outer surface of the body for about half of the length of the body.

The thickness of the body 9 increases along the tapered regions 11 from the junction with the end of the shaft to the upper end of the tapered regions such that the tapered regions form linear ramped surfaces 12 along the longitudinal axis of the body. In the embodiment shown, three tapered regions are shown which are equidistantly spaced around the body but any number of regions may be provided depending upon the number of cutting blades 4 provided on the underreamer.

One longitudinal edge 13 of each ramped surface is undercut into the body. This forms a longitudinal tang 14 which overlies one side edge of the ramped surface 12 to provide one part of an engaging mechanism as will be further described below.

The mandrel 5 is fixedly mounted within the housing 2 of the underreamer such that each longitudinal slot 3 in the housing is lined up over one of the ramped surfaces 12 of the body of the mandrel.

An actuation sleeve 15 is mounted within the housing and lies between the outer surface of the inner mandrel 5 and the inner surface of the housing 2.

An actuating member which in the present embodiment is in the form of a spring (not shown) is provided around the shaft 6 of the mandrel and between the shaft and the actuation sleeve. The spring abuts at one end against the lower surface of the annular rim 8 of the collar and at the other end against the lower end (in use) of the actuation sleeve 15. In this embodiment, the sleeve 15 is closed at the lower end to provide a reaction surface for the spring but in other embodiments the spring may be otherwise operatively connected to the lower end of the sleeve.

A mounting means 18 which in the embodiment shown is in the form of a generally rectangular block is connected to an upper end (in use) of the sleeve 15 and operatively connects a cutting blade 4 of the underreamer to the actuation sleeve 15. The mounting blocks may be integrally formed with the sleeve or may be connected to the sleeve such as for example by cooperating fixing means such a bolts passing through corresponding apertures in the sleeve and the blocks.

An equivalent number of cutting blades 4 and mounting means 18 are provided to the number of longitudinal slots 3 in the housing such that a cutting blade sits within each slot. Therefore, in the embodiment shown, three mounting means would be attached to the actuation sleeve, each connected to a cutting blade of the underreamer.

A jetting nozzle 19 is formed into each of the mounting blocks to enable fluid to be selectively jetted over the cutting blades of the underreamer.

The upper end of each mounting block, remote from the actuation sleeve is formed with a T-slotted head 20 which extends longitudinally beyond the end of the block.

Each cutting blade 4 comprises a substantially rectangular arm with a plurality of cutting elements 21 mounted on the upper surface of the arm.

The thickness of the arm is greater than that of the T-slotted head 20 of the mounting block as will be described further below.

The lower end (in use) of each blade has a substantially rectangular channel 22 formed therein within which the T-slotted head 20 of a mounting block is slidably received. The opening 23 to the channel has a reduced width to retain the T-slotted head of the mounting block in contact with the end of the blade whilst preventing the T-slotted head of the mounting block from backing out of the channel. However, the head 20 of the mounting block can slide vertically within the channel such that the surface of cutting blade can be raised above the surface of the block whilst the head of the block is secured within the channel of the blade.

As shown in FIG. 4, a recess 24 is formed the underside of one longitudinal edge of the cutting blade 4. The recess extends about one third along the width of the blade and along most of the length of the blade. A longitudinal slot 25 is formed at the upper internal edge of the recess along the length of the blade. The longitudinal slot 25 has a height of about half that of the recess 24 and this forms a longitudinal projection 26 which extends along the underside of the blade.

The depth and thickness of the longitudinal slot 25 corresponds closely to that of the longitudinal tang 14 in the edge of the ramped surface 12 of the body such that the tang of the body can be received within the longitudinal slot 25 to allow the blade 4 to slide up and down the ramped surface whilst remaining at all times mechanically secured to the body.

The length of the longitudinal slot 3 of the housing defines the extent of longitudinal movement of the connecting block and the blade with respect to the body.

The operation of the underreamer will now be described starting from the retracted position shown in FIG. 1. In this position, the actuation sleeve 15 is held at the lower position within the housing by the spring, the mounting means 18 are positioned at the lower end of the longitudinal slots 3 in the housing and the cutting blades 4 are positioned at the bottom of the ramped surfaces 12 of the body 9.

In this condition, the cutting blades 4 sit within the longitudinal slots 3 in the housing but the upper surface of the blades, upon which the cutting elements 21 are mounted, lie beneath the upper edge of the longitudinal slots and below the outer surface of the housing. Therefore the underreamer can be inserted through casing with an internal diameter which is greater than the outer diameter of the closed underreamer and can be manoeuvred down the borehole to the selected depth using known techniques.

When the underreamer reaches the required depth at which expansion of the bore hole is required, the drive sleeve 15 is operated by a known means such as a drop ball or flow of fluid through the body or electronic activation such as pump on/off as will be fully appreciated by the skilled person.

Upon actuation the sleeve 15 is forced upwards within the housing 2 against the force of the spring, compressing the spring between the lower end of the sleeve and the rim 8 of the collar of the mandrel. Upward movement of the sleeve pushes the mounting blocks 18 upwards within the longitudinal slots 3 such that they slide over the shaft 6 of the tubular mandrel and move towards the body 9 at the upper end of the shaft. As the blocks move along the shaft, the blades 4 are pushed forwards and begin to move up the ramped surfaces 12 of the body. The blades are prevented from lifting out of contact with the body 9 by the interengagement of the tang 14 on the upper surface of the body in the longitudinal slot 25 in the underside of the blade.

Movement of the blades 4 along the ramped surfaces 12 lifts the upper surface of the blades carrying the cutting elements out of the slots 3 in the housing and thereby increases the outer diameter of the body. As the blades continue to move along the ramped surface, the T-slotted head 20 of the blocks remains in the channel 22 in the lower end of the blades but the cutter rises through the slot as best illustrated in the enlarged view of FIG. 6.

As the upper surface of the blades rise through the slots 2 the under surface of the blades remains at all times in full contact with the ramped surfaces 12 of the body. This prevents material which is removed from the wall of the well bore by the cutting arms from becoming entrained between the underside of the blades and the body which could prevent the blades from being withdrawn back into the housing of the tool.

In the fully extended position, the upper end of the T-shaped head of the mounting blocks rests against the shoulder 10 between the shaft and the body of the mandrel 5.

The underreamer is now in the open position which is shown in FIG. 2 and in this position, the blades stand proud of the slots in the outer housing such that the effective diameter of the underreamer is increased and the cutting elements on the blades are exposed to the wall of the bore. Rotation of the tool in this condition removes material from the inner wall of the bore at the selected depth and increases the inner diameter of the bore.

When the cutting operation is complete and the tool is to be moved to a new depth for additional operation, or alternatively to be withdrawn from the well bore, the upward force on the sleeve 15 is removed, for example in the embodiment controlled by electronic activation, returning to a pump off condition releases the upward force on the activation sleeve and the spring force returns the sleeve to the lower position within the housing.

As the sleeve moves downwards, the mounting blocks 18 are pulled back with the sleeve 15 from the shoulder of the shaft and the body. This in turn pulls the blades 4 back down the ramped surface 12 of the body. As the blades slide back along the ramped surface, the outer surface of the blades falls back into the slots in the housing and the blades retract radially with respect to the mounting blocks.

As with operation from the closed to the open condition of the underreamer, during operation from the open condition to the closed condition the underside of the blades 4 remain in full contact with the ramped surface of the body such that material removed from the inner wall of the well bore can not become trapped between the two which could prevent the blades from returning to the closed, withdrawn position.

It will be appreciated that in the present invention, the weight of the actuation mechanism of the underreamer is carried below the blades and this ensures that upon moving the tool from the open to the closed position, the actuation sleeve is assisted by gravity acting on the sleeve, the mounting blocks and the cutting elements which acts as a bias to returning the tool to the closed position in which it can be recovered from the well bore.

Furthermore, the direct relationship between movement of the actuating sleeve and the longitudinal movement of the cutters along the ramped surface of the body and radially outwardly of the slots in the housing, cuts down on frictional losses in the tool and leads to improvements in design and operating costs.

As a further advantage of the present invention, it is possible to drift the arms of the underreamer against a casing shoe provided at the lower end of the casing string in order to retract the cutters from the expanded to the retracted position in the event that the actuation mechanism fails.

It will therefore be appreciated that the tool of the present invention provides a simplified design in comparison to known underreamers whilst also providing significant benefits and advantages in respect of operation of the tool and particularly in avoiding entrapment of materials removed from the inner surface of the wellbore between the blades and body of the tool.

The tool has been described as comprising three cutting blades which extend through three slots in the housing of the tool but it will of course be appreciated that any number of cutting blades and slots may be provided in any arrangement within the tool. Furthermore, a tool may be constructed in which several sets of longitudinal slots are provided at different positions along the length of the tool with a set of cutting blades slidably mounted in each set of slots. The mandrel 5 may therefore be formed with a plurality of sets of ramped surfaces at spaced intervals along the body. This would allow a cutting operation to take place at several depths at once upon rotation of the tool. 

1. A downhole tool comprising: a body having a slot therein; a cutting blade mounted within the body and extendible and retractable through the slot such that the outer diameter of the tool can be selectively increased; an actuation member for driving the cutting blade between the retracted and extended positions; a mounting means connecting the blade to the actuation member; and said body having a tapered surface along which the blade travels such that as the blade travels along the tapered surface the blade moves radially outwardly with respect to both the body and the mounting means whilst remaining in contact with the tapered surface.
 2. A downhole tool according to claim 1, wherein the tool comprises a plurality of slots and a plurality of cutting blades, each blade being extendible and retractable through a respective slot in the body.
 3. A downhole tool according to claim 2, wherein the slots are equispaced around the outer surface of the body.
 4. A downhole tool according to claim 1, wherein the or each slot in the body extends longitudinally along the length of the body.
 5. A downhole tool according to claim 1, wherein the mounting means comprises a substantially rectangular block
 6. A downhole tool according to claim 5, wherein the block is formed with a T-slotted head at one end.
 7. A downhole tool according to claim 6, wherein the cutting blade comprises a recess at one end which receives the T-slotted head of the block.
 8. A downhole tool according to claim 5, wherein the depth of the or each cutting blade is greater than the depth of the block.
 9. A downhole tool according to claim 1, wherein the cutting blade(s) and body are slidably connected together.
 10. A downhole tool according to claim 1, wherein the or each blade is fixed along one longitudinal edge to the body.
 11. A downhole tool according to claim 1, wherein a channel is formed in one of the underside of the cutting blade and the tapered surface of the body
 12. A downhole tool according to claim 11, wherein a cooperating leg is formed on the other of the cutting blade and tapered surface of the body, the leg being slidably constrained within the channel to prevent the blade being lifted out of engagement with the body as the blade slides longitudinally along the tapered surface.
 13. A downhole tool according to claim 1, wherein the mounting block further comprises a jetting nozzle.
 14. A downhole tool according to claim 1, wherein the mounting block is fixed to the actuation member.
 15. A downhole tool according to claim 1, wherein the actuation member comprises a sleeve.
 16. A downhole tool according to claim 15, wherein the sleeve is slidably mounted within the body of the tool and is selectively operable between a retracted and an extended position within the body.
 17. A downhole tool according to claim 15, wherein the sleeve is operated by a drop ball mechanism.
 18. A downhole tool according to claim 1, wherein the tapered surface comprises a ramp.
 19. (canceled) 